Field of the Invention
The present invention relates to a thermoelectric conversion module in which a plurality of P-type thermoelectric conversion elements and N-type thermoelectric conversion elements are combined and arranged and a thermoelectric conversion device using the thermoelectric conversion module.
Priority is claimed on Japanese Patent Applications No. 2015-190273 filed Sep. 28, 2015 and No. 2016-179109 filed Sep. 14, 2016, the content of which is incorporated herein by reference.
Description of the Related Art
A thermoelectric conversion module has a structure in which a plurality of combinations in which a pair of a P-type thermoelectric conversion element and an N-type thermoelectric conversion element are connected with each other at electrodes are electrically connected in series by arranging them in alternate order of P, N, P, N between a pair of wiring substrates. In such thermoelectric conversion module, when both the ends are connected to DC power source and direct current flows therein, heat is moved in each thermoelectric conversion element by a Peltier effect (the heat is moved in the same direction with the current in the P-type element, and in the opposite direction to the current in the N-type element).
Alternatively, by arranging the thermoelectric conversion module in a state in which one of the wiring substrates is at a higher-temperature side and the other is at a lower-temperature side so as to apply difference in temperature between the wiring substrates, electromotive force is generated in each thermoelectric conversion element by a Seebeck effect and electric current flows. Accordingly, the thermoelectric conversion module can be used for cooling, heating, or generating electric power.
Thermoelectric conversion performance of the P-type and N-type thermoelectric conversion elements is shown by a dimensionless performance index called ZT, which gives a standard for selecting elements. However, even though the elements are made from the same mother material and under the same usage-environment temperature, there are many cases in which the P-type and N-type elements do not always show a same thermoelectric conversion performance; accordingly, the elements need to be adjusted.
For example, Patent Document 1 describes to form elements, generally having square pillar shape with a square cross-sectional shape, into a rectangular cross-sectional shape; and to form the elements into different shapes in accordance with each carrier density of the P-type and N-type elements.
Patent Document 2 describes, when soldering a thermoelectric conversion element onto a warped substrate, to alter thicknesses of solder layers in accordance with a distance between the substrate and the thermoelectric conversion element.
In order to obtain thermoelectric conversion performance (ZT) nearly to each other for the P-type and N-type thermoelectric conversion elements under the same usage temperature environment, it may be considered to select the P-type and N-type thermoelectric conversion elements made of different mother material. However, since strengths of crystal of elements and thermal expansion coefficients are different between different materials, damage to an element having lower strength is larger, i.e., the element having lower strength is broken ahead.
Accordingly, Patent Document 3 suggests a thermoelectric conversion module in which a stress-relaxation layer made of Cr—Cu alloy is formed between a thermoelectric conversion element and an electrode.
However, even though the stress-relaxation layer made of Cr—Cu alloy is used, it is not sufficient to prevent cracks and the like in the thermoelectric conversion element.